This invention relates to a device designed to hook pieces, in particular printed circuit boards, onto transport lines present in tunnel kilns or similar kilns.
The device in accordance with the invention can be classified among the equipment used to manufacture electronic cards or printed circuits, and in particular among the equipment used during the circuit firing stage in a kiln.
The manufacture of printed circuits such as those of computer boards uses photographic processes to make the tracks or pattern of the circuit on a base plate, which consists of one or more layers of copper or other conductive material.
For this purpose a layer of material sensitive to ultraviolet light, for example, is spread on the plate; that layer is photographically exposed, and the plate is then introduced into baths that dissolve the unexposed layer and the underlying layer made of conductive material to produce the circuit tracks.
These known procedures comprise various stages; including the stage when the said sensitive layer is fired, during which the plates that constitute the circuit base are introduced into a kiln, usually the tunnel type, in which the coating layer is xe2x80x9cfiredxe2x80x9d.
For the purpose of firing, each card is passed one or more times through a tunnel kiln together with other similar cards.
The existing conveyor equipment for the firing of rigid printed circuits allows the circuit boards to be introduced in succession into supports constituted by structural shapes arranged transversely on a conveyor belt situated in the lower part of the route, so that the boards maintain a vertical position as they advance through the kiln.
This type of equipment, which is used to handle basically rigid printed circuits, does not need to be fitted with restraint and gripping mechanisms, and is consequently unsuitable to support or move the more recent flexible circuits, as in this case the boards cannot maintain a vertically leaning position, and must therefore be hung from a transport line installed in the upper part of the tunnel and fitted with gripping jaws.
The main drawback encountered with the use of known systems for the transport of flexible printed circuits is that they use complex, bulky jaw assemblies, each of which is associated with pneumatic drive devices; this increases the cost of manufacture and also restricts the number of printed circuits that can be hung from the conveyor, due to the excessive bulk of these gripper activation devices.
The invention provides a new gripping system for the advance of flexible printed circuits through a tunnel kiln or the like, the main objective of which is to reduce the complexity of manufacture, thus limiting both production costs and overall dimensions, as the components of the hooking parts are simplified.
The immediate advantage of the proposed system is that the reduction in overall dimensions leads to a considerable increase in the carrying capacity of the conveyor line and in the number of circuits that can be treated simultaneously on the same line.
A further advantage of the innovation in question is that it features a new gripping system which eliminates components secured by screws or other screwing systems; such components, which are present in known hooking devices, can generate critical situations such as breakage or jamming of the gripping parts when they pass through the kiln at high temperature. These particular purposes, advantages and functions are all achieved, in accordance with this invention, by a device for hooking pieces, in particular printed circuits, to transport lines present in tunnel kilns and the like, in accordance with which shaped supports are fitted transversely to a conveyor belt, slat conveyor or the like, the said supports being constituted by roughly U-shaped guides fitted with elastic systems designed to maintain in the thrust position a pair of pins with sharp corners at the ends, which constitute the elements that grip the printed circuit.
The said elastic systems, subjected to the action of pistons which control their movement, enable the said pins to be maintained in the thrust position during the stages of gripping the circuit, and retracted for a certain distance during the loading and unloading stages.